This invention relates to rotary load counterbalancing mechanisms and more particularly, although not exclusively, to tilt mounting heads for counterbalancing the torque caused by the out of balance mass of a camera or the like mounted thereon when rotated about the tilt axis.
Many load counterbalancing mechanisms are known including hydraulic or pneumatic devices and springs loaded through lever or cam arrangements. Our UK Patent Specification No. 2102757 discloses a multiple spring and lever arrangement which provides true balance and is also capable of adjustment to accommodate different loads but is relatively complex and bulky and can therefore be difficult to accommodate. An important requirement of a counterbalancing mechanisms and particularly mechanisms to be embodied in a tilt mounting for a camera is that the mechanism should be compact so that the overall bulk of the mounting can be kept to a minimum.
WO-A-94/07080 discloses a tiltable mounting for a payload comprising a base and a support member for supporting the pay load. The support member is tiltable about a horizontal axis on the base for tilting about each side of a top dead centre position about said horizontal axis. Torque generating devices are mounted on the base and act on the tiltable support to generate a torque in response to tilting of the support equal and opposite to the outer balance moment of the support with its payload to hold the support balanced in any position of movement about said axis. The tiltable support has two stub shafts on which the support is mounted for tilting about said horizontal axis and two torque generating units are provided which act on the respective stub shafts, each of which provides a torque which varies sinusoidally with displacement. A control is provided for adjusting the torque generating unit for varying the phase angle between the units to vary the collective amplitude of the torque developed by the units for any position of movement of the tiltable torque member to suit the weight of the payload on the support member.
This invention provides a rotary counterbalancing mechanism comprising an input rotatable about a horizontal axis for carrying a mass and means to generate a counterbalancing torque when the input is rotatably displaced from a neutral position in which the mass is disposed vertically above said horizontal axis, wherein the means for generating the counterbalancing torque comprise a pair of aligned linearly moveable outputs, means to convert rotation of the input from said neutral position into sinusoidal displacements of said outputs which are 90xc2x0 out of phase with each other, between minimum and maximum displacement positions, and spring means for resisting said oscillating movement of the outputs away from said minimum displacement positions.
Preferably the means to convert rotary motion of the input into linear movement of said two outputs comprise a rotatable cam mounted to rotate with said input about said horizontal axis and the outputs comprise two cam followers engaging the cam on opposite sides thereof and mounted for linear movement along a common line of action with each other which passes through the axis of rotation of the cam, said spring means acting on the respective followers biasing the followers towards the cam to resist rotation of the cam.
More specifically, providing said minimum displacement positions for the outputs at a recess at the top of the heart and at the base of the heart.
In any of the above arrangements, the spring means may be arranged to resist the movement of the cam followers in compression.
In one particular example according to the invention, the spring means are arranged parallel to one another with one end of each spring means anchored and the other end coupled to a respective cam follower.